Table of Contents

Overview

Delaware’s Sea Level Is Rising

The sea level off Delaware’s coast is up to 4 inches higher than it was in 1956.1 This increase is mostly due to land sinkage2 and ice melt.3 Solutions in Delaware can be complicated because all 3 counties and over 50% of the state’s cities are at risk and need solutions for sea level rise and flooding.4 The state is planning over $60 million in sea level rise solutions, which include wetland renourishment and flood prevention projects.

Sea level rise is speeding up

The sea level around Reedy Point, Delaware, has only risen by 4 inches since 1956. Its speed of rise has accelerated over the last ten years and it’s now rising by about 1 inch every 10 years.1 Scientists know this because the sea level is measured every 6 minutes using equipment like satellites, floating buoys off the coast, and tidal gauges to accurately measure the local sea level as it accelerates and changes.6

Created with Highcharts 6.2.0

Sea level measurement from Reedy Point area tide gauge since 1956

Causes & Complications

Why Are Sea Levels Rising?

While there are four causes of sea level rise in Delaware, land sinkage and ice melt are the largest contributors. Because the rate of ice melt has been increasing significantly since 1992,2 and the land is getting lower each year due to a process called subsidence,3 Delaware is vulnerable to an increased rate of sea level rise in the future. Click here to learn more about these causes.

How Ice Melt Increases Sea Level Rise

How Land Sinkage Increases Sea Level Rise

Most flooding happens in the fall

King tides are unusually high tides that are created during months when the sun, moon, and earth align. The combined gravitational pull of the moon and the sun creates much higher tides, called king tides. In some places, king tides are brought on by changes in the weather and ocean patterns. In places like Reedy Point, king tides are are typically over a foot higher than normal high tides.1 Add that to the 4 inches of sea level rise since 1956 and you end up with flooding even on sunny days.

Solutions aren’t simple

Solving for sea level rise can be complicated in Delaware because over 50% of the state’s cities are at risk or already feeling the impacts of sea level rise and flooding. This can make assessing vulnerability and determining mitigation projects a lengthy process, as all three counties in the state are affected and plans will need to be made for many separate municipalities.4 It will also affect any budgeting done for projects by the state, as funds will need to be spread out across all flood-affected communities.

Forecast

What's the Future of Sea Level Rise?

In the last decade, the speed at which Delaware’s sea level is rising has increased, and is now rising by as much as 1 inch every 10 years.1 Around Reedy Point, it took 35 years for the sea level to rise around 6 inches.1 Scientists now forecast that in just the next 14 years, the sea level will have risen by another 6 inches.7

Scientists are not certain how fast the ocean will warm and ice will melt. They expect water levels to continue to rise faster, but are not sure just how fast. Therefore scientists from the National Oceanic and Atmospheric Administration (NOAA) and the US Army Corps of Engineers (USACE) have made predictions based on ranges from low to high.

Below you can see the range of the NOAA and USACE high and intermediate forecasts for various locations around Delaware.8 Currently, the USACE high forecast, seen as the darkest red line, is the most likely projection.

Reedy Point

Created with Highcharts 6.2.0Reedy Point Sea Level Rise Forecasts

Flooding

Why Are Floods More Frequent?

When the ocean rises high enough, high tides cause flooding even on sunny days. Even though the sea level has only risen by around 3 inches, tidal flooding has increased by 260% in some areas of Delaware since 2000.9

How sea level rise affects Delaware

Flooding even when there’s no rain

Drainage systems are designed to channel excess rainwater from the streets and drain it into the sea. But with the pressure from rising sea levels and higher tides, seawater can get pushed into these pipes and spill out into the streets. This causes flooding even on days without rain.

Drainage Under Normal Tidal Conditions

Drainage With High Tide / Sea Level Rise

Increased storm surge flooding

Unfortunately, slightly higher sea levels make hurricanes even more damaging. Just a few more inches of sea level rise allow a hurricane to push more water onto the land, even if the hurricane itself doesn’t make landfall.

Hurricane Sandy, 2012

Higher sea levels create a higher launching point for storm surge. These small changes in sea level rise are enough to turn what were 100-year storm surges into much more frequent events. In fact, in a third of 55 coastal sites studied throughout the US, 100-year storm surges will be 10-year or more frequent events by 2050.10

This means that in many coastal cities, if you bought a house with a 30-year mortgage today, by the time you paid off your mortgage you could be experiencing extreme 100-year storm surges ten times more frequently due to sea level rise alone. This does not include the added risk of more intense storms resulting from warmer water and a warmer atmosphere, which could further increase storm surge damage.

In 2012, Hurricane Sandy hit Delaware after make landfall in New Jersey, and brought with it powerful storm surge and nearly $7 million in damage to the state.11 Without sea level rise, Hurricane Sandy’s storm surge of around 6 feet would have been much lower.12

Hurricane Sandy, 2012

Costs

What's at Risk in Delaware?

There’s a lot at risk from sea level rise and flooding in Delaware, particularly because the state has the lowest mean elevation in the U.S. This puts the state’s 381 miles of shoreline at great risk.13 Sea level rise is already causing Delaware to lose one acre of tidal wetlands every day14 and based on current projections, the state could face losing 11% of it’s land mass due to beach erosion, which is progressing at a rate of over 3 feet per year.15 The Delaware Estuary is also at great risk, which supports over 500,000 jobs with over $10 billion in wages annually in Delaware and surrounding states.16

BEACHES

Rising seas increase the speed of beach erosion, pulling more sand from the beach into sea. Replacing the sand is possible, but expensive.

COASTAL WETLANDS

BUSINESS & ECONOMY

Flooding can damage sales, shop interiors, and merchandise, and force businesses to close. Tourism and port industries can be impacted or shut down by sea level rise.

Delaware is spending over $60 million on solutions

Some cities have sufficient resources to deal with this problem while others do not. Delaware will need solutions at the individual, local, state, and federal levels to protect its coastal communities.

Prime Hook

The Prime Hook National Wildlife Refuge has embarked on one of the largest marsh restoration projects in the eastern U.S., with a cost of $38 million.17

Wilmington

Wilmington has a $26.5 million project that will create a combined flood basin and wetland park intended to protect the low-lying neighborhoods of Southbridge from flooding.18

South Wilmington

Nearly $3 million will be spent on wetland flood prevention through the South Wilmington Wetland Project.19